1. High resolution X-ray diffraction data have been collected for an aspartyl protease from Rhizopus chinensis, a renin analog. Several renin inhibitors have been analyzed bound to this enzyme. The structure suggests a mechanism of action. 2. The X-ray diffraction analysis of tryptophan synthetase from Salmonella typhimurium has been continued. X-ray data to 2.8Angstrom for the protein and four heavy atom derivatives have been measured and a preliminary analysis to determine the three-dimensional structure is underway.